forked from luck/tmp_suning_uos_patched
locking/mutexes/mcs: Correct barrier usage
This patch corrects the way memory barriers are used in the MCS lock with smp_load_acquire and smp_store_release fucnctions. The previous barriers could leak critical sections if mcs lock is used by itself. It is not a problem when mcs lock is embedded in mutex but will be an issue when the mcs_lock is used elsewhere. The patch removes the incorrect barriers and put in correct barriers with the pair of functions smp_load_acquire and smp_store_release. Suggested-by: Michel Lespinasse <walken@google.com> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Jason Low <jason.low2@hp.com> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1390347353.3138.62.camel@schen9-DESK Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -136,9 +136,12 @@ void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
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return;
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}
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ACCESS_ONCE(prev->next) = node;
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smp_wmb();
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/* Wait until the lock holder passes the lock down */
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while (!ACCESS_ONCE(node->locked))
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/*
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* Wait until the lock holder passes the lock down.
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* Using smp_load_acquire() provides a memory barrier that
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* ensures subsequent operations happen after the lock is acquired.
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*/
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while (!(smp_load_acquire(&node->locked)))
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arch_mutex_cpu_relax();
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}
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@ -156,8 +159,13 @@ static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
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while (!(next = ACCESS_ONCE(node->next)))
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arch_mutex_cpu_relax();
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}
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ACCESS_ONCE(next->locked) = 1;
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smp_wmb();
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/*
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* Pass lock to next waiter.
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* smp_store_release() provides a memory barrier to ensure
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* all operations in the critical section has been completed
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* before unlocking.
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*/
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smp_store_release(&next->locked, 1);
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}
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/*
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